1. Field of the Invention
The present invention relates generally to inertial shakers, and more particularly to an eccentric weight shaker head for use in harvesting fruits, nuts, and the like from trees.
2. Description of the Prior Art
The ability to remove fruit and nuts by shaking the trunk or limbs of a fruit-bearing tree is well known. Heretofore, various mechanical devices for engaging and imparting vibrational energy to a tree have been developed.
Perhaps the most simple shaker mechanism is a jaw or a clamp having a single eccentric weight rotatably mounted thereon. By clamping a portion of the tree, typically the trunk or a large branch, a circular vibration pattern can be induced by rotating the eccentric weight in either direction. Although the frequency and amplitude of vibration may be varied by changing the speed of rotation, it has been found that such a circular vibration pattern often allows a large portion of fruit or nuts to remain on the tree, particularly with nuts such as almonds which are firmly attached to the tree.
By mounting a pair of eccentric weights on the clamping mechanism, the vibrational pattern induced in the tree can be varied depending on the manner in which the weights are driven. Most commonly, the weights are driven synchronously, to induce a linear vibrational pattern. U.S. Pat. Nos. 3,221,567 and 3,548,578 disclose examples of such machines.
When employing two eccentric weights, variable patterns may be induced in the tree by providing weights having different masses, by driving the eccentric weights nonsynchronously, or by nonsynchronously driving weights having different masses. Such sytems are disclosed in U.S. Pat. Nos. 4,170,100; 3,640,508 and 3,548,578.
While a variety of distinct shaking patterns can be achieved with the prior art shaking mechanisms cited hereinabove, it is typically found that use of a single shaking pattern will leave fruit remaining on a tree even after extended periods of shaking. This is true even where the shaking pattern comprises two distinct patterns superimposed by a pair of separately rotated eccentric weights. In general, fruit remains on the tree because portions of the branch system (referred to as nodal locations) remain stationary while the tree is being vibrated. While this condition is somewhat alleviated by a variable amplitude, variable frequency shaking pattern, it is not eliminated entirely.